This invention relates to the field of a new and improved inside blowout preventor.
Use of back pressure or check valves connected in a drilling string to automatically control well blowouts inside the pipe or drill string has previously been undesirable during drilling operations because of the tendency to restrict the flow of circulating drilling fluid and to interfere with the running of other well tools through the bore of the drill string. These valves operated in response to the pressure in the bore of the drilling string which required that the drilling string be filled with drilling fluid from above the valve as the drill string was lowered into the drill hole increasing non-productive trip time. When used in continuous drilling operations these valves also tended to be eroded or otherwise worn or damaged by the circulating drilling fluid wherein they were often rendered inoperable to block flow up the bore of the drill string when required to do so. This problem of reliability was especially true of the inside blowout preventers that were initially stabbed into the drill string to control an existing blowout flow and were not removed until after the well pressure was controlled by establishing circulation of denser drilling fluid.